The present invention relates to an electrophotographic toner composition, in particular, to a toner or developer composition used in a copy machine, laser printer or facsimile machine.
U.S. Pat. No. 4,556,624 to Gruber et al entitled "TONER COMPOSITIONS WITH CROSSLINKED RESINS AND LOW MOLECULAR WEIGHT WAX COMPONENTS" discloses an improved, positively charged electrostatic toner composition comprised of a polyblend mixture of a crosslinked copolymer composition and a second thermoplastic polymer, pigment particles, a wax component and a charge enhancing additive.
U.S. Pat. No. 4,557,991 to Takagiwa et al entitled "TONER FOR DEVELOPMENT OF ELECTROSTATIC IMAGE CONTAINING BINDER RESIN AND WAX" discloses a toner for development of electrostatic image which is comprised of a resin binder selected from a polyester resin, a vinyl polymer, a styrene-butadiene copolymer, etc. and a wax, wherein the wax is comprised of a polyolefin which has been block copolymerized or grafted copolymerized with an aromatic vinyl monomer.
Generally, the development of electrophotography consists of the steps of: (a) the distributing of electricity on a photo conductor, (b) exposure to form an electrostatic image, (c) developing an electrostatic image by using toner composition, (d) transferring the toner onto paper or transparency, (e) fixing the toner onto the paper or transparency, and (f) removing the toner residue from the photo conductor. Generally the fixing method consists of cold pressing and thermal pressing. In the cold pressing method, due to the large amount of wax contained in the toner, the quality of the copied article is poor. In the method of thermal pressing, due to the fact that the toner is in contact with the heated roller, offsetting printing will occur, i.e. during the fixing step the toner will adhere to the heated roller and after that it will print onto the copied paper. To avoiding these drawbacks and prevent the offsetting occurrence, U.S. Pat. No. 4,579,908 instructs on the introduction of silicone oil onto the heated roller. However, in order to carry out this method, the roller is made very complicated and is thus prone to contamination. Therefore, in order to prevent offsetting, it is suggested that no silicone oil or just a little silicone oil be introduced onto the heated roller. Under this requirement, it is desired that the toner have the anti-offsetting property.
In some prior references, such as U.S. Pat No. 4,206,247 and 4,556,624, it is suggested that low molecular weight wax be added to the toner as a releasing agent. The common waxes which can be used, for instance, are polyethylene or polypropylene wax having a molecular weight of 1000 to 5000. The amount of wax added to the toner ranging from 2% to 20%, preferably 5% to 10%. The addition of the low molecular weight wax will solve the problem of offsetting, however, the low melting point and high adhesive property of the wax may cause the following drawbacks: (A) The toner will adhere onto the developing sleeve of the coping or printing apparatus, (B) poor storage, i.e. the toner will form an agglomeration after a period of storage, and (C) the flowability of the toner is poor. Due to the aforementioned drawbacks, the quality of the print is poor. In order to upgrade the flowability, hydrophobic silica is added. The amount added is about 0.5%. However, silica is a very hard material, thus the photo sensing rod may easily be scratched. In particular, the currently used organic photo sensing body will be scratched. Besides, the electrical resistance of the silica is relatively low, and thus the resolution of the copied pattern will be lowered.
In order to upgrade the flowability of the low molecular weight, U.S. Pat. No. 4,557,991 discloses the use of polyethylene grafted aromatic monomer to substitute for the commonly used low molecular weight wax. However, the grafted polyethylene wax and the toner resin are good compatible pairs, and thus the releasing property is poor. As a result, the amount of the grafted aromatic monomer must be increased so as to produce an anti-offsetting effect. In addition, the cost of polyethylene grafted aromatic monomer is higher than that of the common low molecular weight wax. This will causes an increase in the cost of the toner composition.